in the morning on gma. We move on to the stomach bug now sickening 285 people across 11 states, sending 18 people to the hospital. What's puzzling health official system how this illness found its way to the u.S. Here's dr. Richard besser tonight. We don't know a lot about this rare outbreak, but we do know more people are getting sick. With cyclospora, a parasite. 285 people so far, and the list of states is growing. St week, then nine, and today, two more -- ohio and minnesota. It travels on food. But which kind, we don't know. Past culprits have been snow peas, berries, basil. But always on food imported from outside the u.S. It becomes a stow-away in your body, and about a week after you eat it, the stomach pain and diarrhea begin. Sometimes there's weight loss, bloating, and fatigue. And without treatment, you may feel it for a month. The big take away is if you have these symptoms, there's only one antibiotic that's going to help you, so you need to ask to get tested. That's very important. Ask the doctor if you're concerned at all. Exactly. Thanks, rich.

This transcript has been automatically generated and may not be 100% accurate.

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